Technical Field
The present invention relates to an intermediate transfer belt and an image forming apparatus using the belt.
Description of the Related Art
Conventionally, a seamless belt is used in various applications as a member in image forming apparatus. Particularly, in recent full-color image forming apparatuses, intermediate transfer belt methods overlapping four color, i.e., yellow, magenta, cyan and black developed images on an intermediate transfer medium once, and transferring the overlapped full-color images on a transfer medium such as papers at a time are used.
The intermediate transfer belt is produced by a batch production method using a curing resin and a continuous extrusion method using a thermoplastic resin. It is already known that the continuous extrusion method using a thermoplastic resin is advantageous to reduce environmental load and cost. The thermoplastic resin has an elasticity of from 1,000 MPa to 4,000 MPa when molded into an intermediate transfer belt. However, the belt having an elasticity not less than 2,000 MPa has high surface hardness, resulting in being easy to crack, difficult to stably mold, and needing high molding temperature although having high scratch resistance and producing no stripe images. Therefore, the thermoplastic resin preferably has an elasticity of from 1,000 MPa to 2,000 MPa when molded into an intermediate transfer belt.
However, although reducing environmental load and being low-cost, the belt having an elasticity of from 1,000 MPa to 2,000 MPa has low surface (Martens) hardness, and has scratches and stripes on an inner circumferential surface thereof due to convexities and concavities of rollers such as a drive roller, a suspension roller and a roller opposite to a belt cleaner, resulting in production of abnormal images. For example, when the suspension roller has microscopic convexities and concavities from the beginning or due to adherence of foreign particles, when foreign particles such as a metallic powder and an aggregated toner adhere to the backside of the belt, and/or when scratches are formed on the surface of a roller, convexities and concavities corresponding to the microscopic convexities and concavities, the shape of the metallic powder or the aggregated toner, and/or the scratches formed on the surface of a roller are formed on the surface of the belt.
FIG. 1 is a photograph taken by an optical microscope of an example of scratches formed on an inner circumferential surface of the belt due to convexities and concavities on a roller (200 times). The scratches have a length of from 5 μm to 20 μm and a depth (height) of from 1 μm to 2 μm. The convexities and concavities on the surface of the belt cause stripe images because of poor contact thereof to a toner image. In order to avoid scratches on an inner circumferential surface of the belt, 1) a method of reducing the surface roughness of the suspension roller suspending the belt, 2) a method of placing a cleaning member for one of the suspension rollers to remove foreign particles adhering thereto, 3) a method of making a friction coefficient of the surface of a roller not greater than 0.25 or lower than a friction coefficient of the surface of the belt, and 4) a method of reducing roughness of the backside of the belt are suggested.